Version: 1.17.10 Caves and Cliffs experimental toggle

Expected Result: 
most blocks below Y=0 will be deepslate.

Actual Result
Most blocks below Y=0 are stone, and deepslate will only generate between Y=0 and Y=16

How to replicate:
Create a new world in bedrock 1.17.10 with the caves and cliffs toggle on, and dig down to any Y coordinate below 0.